Imaging devices, such as optical scanners, are well-known in the art and produce machine-readable image data signals that are representative of a scanned object, such as a photograph or a page of printed text. In a typical scanner application, the image data signals produced by an optical scanner may be used by a personal computer to reproduce an image of the scanned object on a suitable display device, such as a CRT or a printer.
A hand-held or portable optical scanner is an optical scanner which is designed to be moved by hand across the object or document being scanned. The hand-held scanner may be connected directly to a separate computer by a data cable. If so, the data signals produced by the hand-held scanner may be transferred to the separate computer "on the fly," i.e., as the image data are collected. Alternatively, the hand-scanner may include an on-board data storage system for storing the image data. The image data may then be downloaded to a separate computer after the scanning operation by any convenient means, such as via a cable or an optical infrared data link.
Hand-held or portable optical scanners are well-known in the art and various components thereof are disclosed in U.S. Pat. No. 5,552,597 of McConica for "Hand-Held Scanner having Adjustable Light Path", U.S. Pat. No. 5,586,212 of McConica, et al., for "Optical Wave Guide for Hand-Held Scanner," U.S. Pat. No. 5,381,020 of Kochis, et al., for "Hand-Held Optical Scanner with Onboard Battery Recharging Assembly," and U.S. Pat. No. 5,306,908 of McConica, et al., for "Manually Operated Hand-Held Optical Scanner with Tactile Speed Control Assembly," all of which are hereby incorporated by reference for all that they disclose.
A typical hand-held optical scanner may include illumination and optical systems to accomplish scanning of the object. The illumination system illuminates a portion of the object (commonly referred to as a "scan region"), whereas the optical system collects light reflected by the illuminated scan region and focuses a small area of the illuminated scan region (commonly referred to as a "scan line") onto the surface of a photosensitive detector positioned within the scanner. Image data representative of the entire object then may be obtained by sweeping the scan line across the entire object, usually by moving the hand-held scanner with respect to the object. By way of example, the illumination system may include a light source (e.g., a fluorescent or incandescent lamp or an array of light emitting diodes (LEDs)). The optical system may include a lens and/or mirror assembly to focus the image of the illuminated scan line onto the surface of the detector. Alternatively, a "contact image sensor" or CIS may be used to collect and focus light from the illuminated scan region onto the detector.
The photosensitive detector used to detect the image light focused thereon by the optical system may be a charge-coupled device (CCD), although other devices may be used. A typical CCD may comprise an array of individual cells or "pixels," each of which collects or builds-up an electrical charge in response to exposure to light. Since the quantity of the accumulated electrical charge in any given cell or pixel is related to the intensity and duration of the light exposure, a CCD may be used to detect light and dark spots on an image focused thereon.
One type of hand-held scanner device may include a position sensing or "navigation" system for determining the position of the hand-held scanner with respect to the object being scanned. Essentially, such position sensing systems allow the scanner to correlate its position with respect to the object being scanned. The position correlation allows a complete image of the scanned object to be produced even though the scanner may not scan the entire object during a single pass or "swipe." For example, if two or more swipes of the object are required to scan the entire object, then the position correlation provided by the navigation system will allow the various portions of the scanned image data to be "stitched" together to form a single unitary image representative of the entire scanned object.
One type of navigation system utilizes a pair of optical sensors to detect certain inherent structural features (e.g., surface roughness, paper fiber orientation, etc.) contained on the object being scanned (e.g., a sheet of paper with text or images thereon). Examples of the foregoing type of navigation system are disclosed in U.S. Pat. No. 5,089,712 of Holland for "Sheet Advancement Control System Detecting Fiber Pattern of Sheet," and U.S. Pat. No. 5,578,813 of Allen, et al., for "Freehand Image Scanning Device which Compensates for Non-Linear Movement," both of which are specifically incorporated herein by reference for all that they disclose.
While such navigation systems are known and are being used, they are not without their disadvantages. For example, significant problems can arise if the user is careless with the operation of the scanner and allows one or more of the navigation sensors to move past the edge of the object (e.g., document) being scanned. If this happens, the navigation system will lose track of its position, which usually prevents the image processing system from properly stitching together the various image portions to form a whole. Another problem associated with navigation systems of the type described above is that it is often difficult for the user to ascertain precisely the location of the bounds of the scan line due to the positions of the optical navigation sensors, which are located at either end of the scan line. Consequently, the user often times fails to provide sufficient overlap of the scanning swipes, which again, can make it difficult or impossible for the scanner control system to stitch together the various image portions to form the unitary whole.
Consequently, a need exists for hand-held imaging device having a navigation system that does not suffer from the disadvantages associated with currently existing navigation systems.